FRIDAY, Feb. 1 (HealthDay News) -- Use of psychiatric medications is most prevalent in the southern United States and least prevalent in the West, according to a new U.S. study.

Although people living in the West are the least likely to use antipsychotics, antidepressants and stimulants, the Yale researchers found that the drugs' use is 40 percent higher in a large section of the South than in other parts of the country. The study authors attributed this discrepancy to variations in local access to health care and marketing efforts within the pharmaceutical industry.

"The geographic patterns we identify are striking and map onto the patterns found for a host of other medical conditions and treatments, from cognitive decline to bypass surgery," Marissa King, assistant professor of organizational behavior at the Yale School of Management, said in a school news release. "Our work suggests that access to clinical care and pharmaceutical marketing may be critical for understanding who gets treated and how they get treated."

The study, which included data on 60 percent of the prescriptions written in the United States in 2008, revealed that patients living in sections of the South were 77 percent more likely to fill a prescription for a stimulant. Southerners also were 46 percent more likely to fill a prescription for an antidepressant and 42 percent more likely to do so for an antipsychotic.

"We identified clear regional clusters where the use of antidepressants, antipsychotics and stimulants was elevated," King noted. "The geography of the cluster for each class of medication was different, but they overlapped each other, with Tennessee as the center point."

At the local level, the researchers also identified significant differences in use of mental health medications. For example, 16 percent of residents of Cape Cod, Mass., used stimulants compared with just 2.6 percent of the population nationwide.

Meanwhile, about 40 percent of residents of Alexandria, Va., took antidepressants. In contrast, roughly 10 percent of the U.S. population used these drugs. Antipsychotics were most commonly used in Gainesville, Fla., where 4.6 percent of local residents took the drugs, compared with a national average of 0.8 percent.

The researchers tracked the regional use of certain medications by analyzing the ZIP code of the doctor who prescribed the medication.

The study was published online recently in the journal Health & Place.